A conventional refrigeration cycle device is formed by connecting the following components in the following order through refrigerant pipes: a compressor that compresses a medium-temperature low-pressure refrigerant (referred to as “medium-temperature/low-pressure,” hereinafter for ease of explanation); a condenser that condenses the compressed refrigerant (referred to as “high-temperature/high-pressure refrigerant,” hereinafter); an expansion valve that expands the condensed refrigerant (referred to as “medium-temperature/high-pressure refrigerant,” hereinafter); and an evaporator that evaporates the expanded refrigerant (referred to as “low-temperature/low-pressure refrigerant,” hereinafter). Hereinafter, such configuration is referred to as “main circuit.” An invention is disclosed that cools the medium-temperature/high-pressure refrigerant to turn into a “supercooled (subcool)” state and then supplies the refrigerant to the expansion valve in order to increase a refrigerating effect at the load side (see Patent Document 1, for example).
On the other hand, the conventional refrigeration cycle device uses an incombustible HFC (Hydrofluorocarbon) refrigerant such as R410A. Therefore, the greenhouse effect of the refrigerant is about 2,000 times greater than that of carbon dioxide. It is indicated that if the refrigerant leaks by accident when the refrigeration cycle is for example disposed of or repaired, the refrigerant remains undecomposed and floating in the atmosphere for long periods of time, contributing to the acceleration of global warming.                Patent Document 1: Unexamined Patent Publication No. H06-331223 (Pages 3 to 4 and FIG. 1)        